A transcanal cochlear implant is ideally suited for the profoundly deaf where conventional amplifying hearing aids are of limited or no value. That is to say, with maximum gain delivered by the most powerful hearing aids, these profoundly deaf individuals cannot hear sound and hence cannot discriminate and understand speech. In addition, an estimated 200–300 million people have various patterns of severe sensorineural hearing loss, which are imperfectly rehabilitated via hearing aids. An example of such is the so called “ski-sloped hearing loss,” where there is near normal hearing in the low to middle frequency range, but the hearing drops out dramatically in the higher frequencies. For these types of hearing loss, amplification is ineffective because the cochlea cannot perform its transductive function of converting the mechanical energy of sound to the electrical current which is ultimately perceived as sound by the brain. The inner ear structures responsible for this transductive function are known as hair cells. The electrical currents which they produce in response to the mechanical stimulation by sound are known as cochlear microphonics. When these hair cells are sufficiently damaged as in the above mentioned scenarios no amount of amplification will be effective.
The cochlear implant is, in effect, a bionic ear in that it replaces the lost cochlear microphonic with an electrical current that is the precise analog of sound. Currently, United States Food and Drug Administration (“FDA”) has approved cochlear implants. The approved cochlear implant are so-called multichannel long electrode devices. They are expensive, highly complex devices that must be surgically introduced via a complicated and (for the average otolaryngologist) risky procedure under general anesthesia known as the facial recess mastoidectomy. The estimated cost of these cochlear implant systems, including surgery, anesthesia, hospital and programming fees is currently quite high. The hardware necessary to program these devices adds further to the high cost. The time to program the first map for these devices averages from four to twelve hours depending upon the age of the patient and other factors. The prohibitive price and impractical complexity deter accessibility to the vast majority of the global deaf population. Furthermore, the average otologist in the developing countries of the world typically does not have the sophistication, expertise and equipment to confidently undertake the facial recess mastoidectomy in order to introduce the internal component of the multichannel systems.
The most tragic irony of all is that the multichannel long electrode devices can destroy residual hearing when they are inserted into the cochlea. This well acknowledged fact makes these devices difficult to justify in very young infants where the precise degree of hearing loss is often in doubt. Furthermore, the electronics package and receiver coil for such a complex sound-processing scheme would not fit within the middle ear space.